If you mean different Tor exit addresses, I think the easiest (and only?) option is to run different Tor instances on different ports, and to have for each Tor instance a different browser (or a different browser profile, for example with Firefox) configured to use that instance.
– PierreApr 24 '14 at 17:39

If someone could explain how to get the other Tor browsers working with the first one's ControlPort, that would be very cool.
– mirimirJul 22 '14 at 20:17

You can achieve this by running multiple Whonix instances: gateway and workstation VMs.
– user3273Jul 27 '14 at 11:46

4 Answers
4

This method launches multiple Tor instances, each with its own SocksPort and ControlPort. This ensures that the Tor Browsers are fully functional, portable, and self-contained. However, someone should confirm that I haven't missed anything that could compromise TBs security.

Optional: Download, verify, and install Tor Browser.

Make copies of the Tor Browser folder with different names (eg. Number them)

Launch Tor Browser

Edit about:config

Modify extensions.torlauncher.control_port to a new ControlPort (eg. 9052 for Tor Browser 2)

Edit TorButton Preferences (without the GUI [removed in 4.5 update])

Modify extensions.torbutton.custom.socks_port (on newer versions this is network.proxy.socks_port) to a new port (eg. 9152 for Tor Browser 2)

Modify extensions.torbutton.custom.socks_host (on newer versions this is network.proxy.socks) to 127.0.0.1

Alternatively, this might be possible with a single Tor instance as the SocksPort and ControlPort. This would require the use of the control_auth_cookie (CookieAuthentication) or HashedControlPassword, and about:config extensions.torlauncher.start_tor=false. However, the browsers would not be self-contained and portable, as they would require a process that isn’t in their own directory.

Inspired by mirimir's answer which seemed to compromise TB's security.

Please Help on Step 7 Step 7- Edit torrc-defaults in \TorBrowser\Data\Tor Change SocksPort to what you set in step 5 Change ControlPort to what you set in step 4 When i open this folder , i can't see "Socksport" and "ControlPort" all i see is file with Type:File ,no one can edit them!
– user7598Jun 7 '15 at 9:50

This answer seems outdated (step 5 particularly), since there's no GUI in Tor Button anymore. Is there an updated way to achieve this ? Furthermore, how does this answer may compromise TB's security ?
– X.LINKApr 25 '18 at 10:27

For TBB 8, skip step 7 (editing torrc-default). Otherwise the control and socks port are configured twice, causing tor to attempt to bind to the control port and socks port twice and fail.
– KevinoidDec 30 '18 at 2:25

Install the first Tor browser as directed. Then change the folder name, perhaps adding "a" or "1" to the end. Now install the second Tor browser, and change its folder name, continuing whatever pattern you've chosen.

Open the second Tor browser, and browse about:config. Search for "torlauncher", and double-click the extensions.torlauncher.start_tor (whichs value is set to true) to toggle it to false. See Tor ticket 6009. I got that reference from the Whonix documentation, by the way.

Now edit ..Browser\TorBrowser\Data\Tor\torrc-defaults in the first Tor browser folder, and add additional SocksPort lines: for example, SocksPort 9152, SocksPort 9153 etc. Save changes and exit the editor. Then start the first Tor browser. Its Tor instance will now handle your other Tor browsers.

Now open the second Tor browser then TorButton Preferences. Select "Use custom settings" then change the SOCKS Port to 9152 and click OK. Browse https://check.torproject.org/ and verify that you're using Tor.

Now close both the first and second Tor browsers. Install the third Tor browser, and change its folder name, continuing whatever pattern you've chosen.

Start the third Tor browser, and browse about:config. Search for "torlauncher", and double-click the extensions.torlauncher.start_tor line to set it to false. Then change its SOCKS Port to 9153, and close it.

Now start the first Tor browser, and then the third Tor browser. In the third Tor browser, browse https://check.torproject.org/ and verify that you're using Tor.

I tried whatever you said in your answer, but unfortunately,mirimir, it didn't work.
– user6682Feb 8 '15 at 11:32

Just change the SOCKS port. Do not set extensions.torlauncher.start_tor=false. That's only if you use a system Tor, which requires setting a control port password too.
– Jeff BurdgesMay 11 '15 at 20:36

(Update: in the recent Tor Browser (December 2019) it is not longer required (neither will work) to modify torrc-defaults. The browser extensions seem to start Tor already with those port settings from user.js. So it is enough to just modify user.js in the browser profile.)

Tor uses default proxy port 8118. Now, you want multiple browsers using the same Tor instance. You have to download Privoxy click here this is use to enable the Proxy port.
To chain Privoxy and Tor, both running on the same system,
change the browser Proxy setting like this:

ip address : 127.0.0.1
port : 8118

Now see if proxy port is running check here
If it is running, you can now make a Tor request using multiple browsers

Tor Browser doesn't use privoxy anymore, and so "Tor uses default proxy port 8118" is no longer accurate. (I wonder if we should just remove this answer so it is no longer a useful one?)
– Roger DingledineMar 9 '16 at 1:02

@RogerDingledine IMHO deleting the answer is appropriate, at least according to meta.stackexchange.com/revisions/11706/2. («If the answer is outdated or no longer relevant either delete it or update it so it is relevant.»)
– myrddApr 8 '18 at 10:48